Buoyant tow and communication line



1951 G. E. FORSBERG 2,577,077

BUOYANT TOW AND COMMUNICATION LINE Filed June 2, 1947 HIGH MOLECULARWEIGHT F G I SAPONIFIED CELLULOSE ACETATE,

CONTINUOUS BODY OF ELECTRIC INSULATING POLYETHYLENE ELECTRIC F 3CONDUCTOR HIGH MOLECULAR WEIGHT SAPOEEIED CELLULOSE ACETATE,

ECTRIC INSULATING 6 FIG. 5 CONT'NUOUS BODY OF POLYETHYLENE 23 24 26 L' 26 ELECT RIC CONDUCTOR INVENTOR aEoRaE E. FORSBERG wmww ATTORNEY PatentedDec. 4, 1951 UNITED STATES PATENT OFFICE BUOYANT TOW AND COMMUNICATIONLINE George E. Forsberg, Worcester, Mass., assignor to SurprenantElectrical Insulation Company, Clinton, Mass., a corporation ofMassachusetts Application June 2, 1947, Serial No. 751,679

4 Claims. (Cl. I'M-101.5)

This invention relates to improvements in buoyant tow and communicationlines for marine operations and it is the general object of theinvention to provide a composite tow line containing relatively heavyelements sufficiently strong to withstand considerable tension inclosedin a light weight water resistant coating or sheath which causes theline to float in water.

In certain naval landing operations it is necessary to connect a smallboat to a mother ship by a tow line which can be reeled in to draw theboat away from enemy fire. Several attempts have been made to providesuch a line, but they have been unsatisfactory either because they didnot have the requisite strength, or the floats used to keep them on thesurface of water interfered with reeling. In order that the small boatmay be under immediate control of the mother ship it is important thatthe tow line be able to float so that it can remain substantiallystraight. The sea floor is not always smooth and may have formationssuch as coral with which a tow line would become entangled if it sank.The line should also be flexible to permit coiling, and should benon-absorbent to prevent increase in weight when immersed.

Itis an important object of the present invention to provide a tow linemade of strong cords or cables heavier than water surrounded and keptdry by an inclosing sheath made of material having a specific gravityless than that-of water and of suflicient size to cause the line tofloat in water.

It is a more specific object of the invention to make the cords orcables of high tensile strength relatively heavy plastic or artificialfibers or filaments and make the sheath of a light weight extrudableplastic. The cables may be made of a saponified cellulose acetate typeof extruded fiber, while the sheath may be made of polyethylene. Thecables carry the greater part of the load, but their stretch orelongation in use is within the elongation limits of the sheath and thelatter remains intact without breaking or cracking.

The occupants of the small boat should be able to communicate with themother ship and to this end it is a further object of the invention toinclose small electric conducting wires within the tow line so thattelephone connections may be maintained between the two vessels.

If enemy fire is such as to require withdrawal of the landing party themother ship will reel in the tow line and the small boat will follow azigzag course to avoid gun fire. In order that such a course may beimpeded as little as possible by the line the latter is so made that itwill lie flat on the water surface and cut the water edgewise as thesmall boat moves first to one side and then the other.

The invention is not limited to tow lines, and may for instance beadapted for use in diving operations.

With these and other objects in view which will appear as thedescription proceeds, my invention resides in the combination andarrangement of parts hereinafter described and set forth.

In the accompanying drawings, wherein two forms of the invention are setforth,

Fig. 1 shows a plan view of the preferred form of the invention adaptedmore particularly for towing operations,

Fig. 2 is an enlarged vertical section on line 2--2, Fig. 1,

Fig. 3 is a detailed view of one of the cords or cables inclosed in thetow line set forth in Fig. 1, certain of the strands being opened out toshow the location of the electric Wire carrying strand.

Fig. 4 is an enlarged transverse section on line 4-4, Fig. 3..

Fig. 5 is a view similar to Fig. 1 but showing the modified form of theinvention adaptable more particularly to diving operations,

Fig. 6 is an enlarged transverse section on line B6, Fig. 5,

Fig. 7 is a view similar to Fig. 3 but showing the cable used with themodified form of the invention, and

Fig. 8 is a diagram indicating how the preferred form of the inventionis used in naval operations.

Referring more particularly to Figs. 1 to 4- which illustrate thepreferred form of the invention, the tow and communication line Lincludes two cords or cables l0 and II spaced from each other andextending side by side throughout the length of the line. Each cable ismade up of several peripheral strands I 2 surrounding a central or innerstrand l3, and each strand is formed of a plurality of filaments orthreads l4 twisted on themselves as indicated in Fig. 3. Each centralstrand I3 may have wrapped therearound a metallic electric conductor 15which may include several separate tin coated copper wires. Eachconductor 15 is insulated by the peripheral strands 12 which are wrappedhellcally around the central strand as shown in Fig. 3. The two cablesl0 and H are inclosed within a water resistant electric insulatingplastic sheath I8 which is lighter than water and is of such size as tocause the line to float in water. Part of the sheath is located betweenthe cables and holds them in spaced substantially parallel relationthroughout the length of the tow line,

see Fig. 2.

In the manufacture of the preferred form of the invention the conductorsor copper wires I5 are first wrapped helically around the centralstrands !3. The other strands 12 are then wrapped around the centralstrands to form a cable. Two cables thus made are then drawn through asuitable die and the solid plastic sheath or jacket I8 is extrudedaround them. Because of this mode of manufacture the tow line can bemade of any desired length, and the sheath l8 fits closely into thespaces between the strands and threads to establish a strong connectionwith them. The wires l need not be present for all uses of theinvention, and may be omitted if telephone commumcation is not needed.As shown in Fig. 2 the width of the tow line is greater than itsthickness and for this reason the tow line can be wrapped on a drum orthe like, and will also tend to lie flat in water.

In Fig. 8 it is assumed that the small boat B is being drawn away fromthe shore S by the mother ship M. The line L will be attached to theboat in any approved manner and the mother ship will have a reel IS onwhich the tow line is wound. When the telephonic signal to withdraw isgiven the ship M will move away from the shore and the boat B will beguided by the occupants to pursue a zig-zag course to avoid enemy fireby manipulating rudder ll. When the boat moves as indicated by dottedline a the tow line will move from the full line to the dotted lineposition. Since the tow line L is flat and floats it will cut the wateredgewise and offer a minimum of resistance to lateral movement as theboat zigt zags.

The modified form of the invention, shown in Figs. 5 to 7, is adaptedmore particularly for use in diving operations to connect the helmet ofthe diver with the ship conducting the diving operation. The line L ispreferably of circular cross section with the strands located centrallythereof, and the electric communicating wires are wrapped around certainof the strands which are spaced from each other by other interposedstrands.

Referring to Fig. 6, the central or inner strand 20 is similar to strandl3 of the preferred form of the invention and has wrapped therearound anelectric conductor 2| similar to conductor l5. Surrounding strand 20 isa group of strands 22 similar to strands l2 of the preferred form. Inaddition, there is a. third group of strands 23 around the inner group,one of these latter strands, indicated at 23a, being similar to thecentral strand in that it is wrapped with an electric conducting wire24. The group of strands 22 is thus located between the wire carryingstrands 20 and 23a to keep the electric conductor wires of these twostrands insulated from each other throughout the length of the line. Thestrands 2|], 22, 23 and 23a together form a cable 25 or more or lesscircular cross section as indicated in Fig. 6. The core 25 is surroundedby a plastic sheath 26 similar to coating or sheath l8 and of suchvolume as to cause the line L to float in water.

The manufacture of the modified form of line L is similar to that of thepreferred form and results in a line the various component parts ofwhich are held in close relationship with each other. The surroundingsheath 26 is embedded partly at least in the strands 23 and 23a, andalso provides insulation for the electric wires, particularly the wirearound strands 23a.

The threads l3 and H of the strands have high tensile strength, and maybe made of deacetylated or cold drawn high molecular weight saponifiedcellulose acetate fibers or filaments which are ordinarily heavier thanwater. In practice I have used a material known in the trade as"Fortisan" having a specific gravity of 1.5, but I do not wish to bethus limited, as any strong and relatively heavy fiber possessing thegeneral properties of Fortisan, such as nylon, can be used to make thethreads. The material of which the cables 10, H and 25 are made W111ordinarily be electric insulating and heavier than water and ofthemselves would sink if used as tow lines unless supported by thesheaths. In order to prevent possibility of chemical action between thefibers and copper wires the latter are coated with tin.

Tne plastic sheath for the cables is lighter than water and is presentin sufficient amount to counteract the tendency of the cables to sink.The sheaths l8 and 26 may be made of a high molecular weight plastic,such as polyethylene, which has sufiicient strength in tension andcompression at ordinary temperatures to withstand the uses to which itis put. Polyethylene has a specific gravity of approximately 0.92 and isflexible, electric insulating, chemically inert, and will stretch atleast as much as the cables in normal use without rupture. Since thesheath has a very low factor of water absorption it keeps the cablesdry.

The form of the invention shown in Fig. 6 has been described as suitablefor diving operations, but by the omission of the electric wires and areduction in size with fewer strands such a cable can be adapted to useas a clothes line. In this connection I have used seven strands, sixaround a central strand, and coated the cable thus formed with a sheathmade of polyethylene. The seven strand cable is similar to one of thecables of the preferred form of the invention without the wires, thefibers of the threads composing the strands being preferably though notnecessarily extruded and having considerable strength. The fibers can besimilar to those used in the tow line form of the invention. For clothesline use the sheath will be relatively thin, and since the cable will becompressible to some extent due to the flexibility of the strands, theclothes line can be deformed slightly by a clothes pin to preventslipping along the smooth surface of the sheath. While this may be adesirable feature in some instances, I do not wish to be limited to it.

In practice I find that polyethylene and similar plastics suitable foruse as described hereinbefore are subject to crazing when exposed tostrong light, such as exists in certain marine areas where landingoperations may be made. Thi crazing is due to penetration of the sheathby light rays, and in order to prevent such penetration I incorporatepreferably opaque coloring matter in the material of which the sheath ismade prior to extrusion thereof. For naval operations the color may be agray which will make the line invisible except at very close range. Fordiving operations a color readily distinguished in water may be used,while for clothes line use a white pigment such as titanium oxide may beused.

The sheath is made of plastic material prefer ably lighter than waterand for this purpose polyethylene is quite acceptable, but it will beapparent that any other sufficiently light weight material, such asexpanded or cellular cellulose acetate, may be used if desired. It willbe sufllcient for the purposes of the invention if the materials ofwhich the line is made are of such volume and weight that the line as awhole has the requisite strength and floats in water. The plastic sheathwhich incloses the cables should be resistant or impervious to water andof good insulating properties when communication wires are used. Thecables carry the greater part of the load and have an elongation whennormally loaded within the elongation limit of the sheath. The lattertherefore does not break or crack when the line is in tension, and thecommunication wires are protected and can be used for telephone purposeswhile the small boat or diver is being reeled in by the mother orattendant ship. Also, the tow line of the preferred form lies fiat onwater and cuts the latter edgewise when the small boat follows a zig-zagcourse.

From the foregoing it will be seen that I have provided a simple towline made of materials chosen for their weight and volume to besufliciently strong to serve as a tow line and also float in water. Thecables are kept dry by the sheath and preserve their strength while theline is in use. Both forms of line can if desired be made with telephonecommunication wires. In the preferred form of the invention two cablesarranged side by side are surrounded by a plastic material impervious toand lighter than water and of suflicient volume to cause the line tofloat. More than two cables can be used if greater strength is desired.The modified form of the invention has a single cable and the electricwires, if used, are wound around strands which are separated from eachother by other strands so that the wires are kept insulated from eachother. The cables can be made of a deacetylated or cold drawn highmolecular weight saponified cellulose acetate. Furthermore, ananti-crazing agent, such as an opaque pigment, may be used to preventcracking or deterioration of the sheath by light. When adapted forhanging clothes the line will be of relatively small cross section butwill otherwise be similar to the form used for diving operations.

Having thus described my invention it will be seen that changes andmodifications may be made therein by those skilled in the art withoutdeparting from the spirit and scope of the invention and I do not wishto be limited to the details herein disclosed, but what I claim is:

1. In a combined communication and tow line, an inner strand heavierthan water composed of a plurality of high molecular weight saponifiedcellulose acetate threads, an electric conductor wrapped around saidstrand, a plurality of peripheral stands heavier than water eachcomposed of a plurality of high molecular weight saponified celluloseacetate threads disposed around said inner strand, and a sheath lighterthan water made solely of a continuous body of polyethylene surroundingand in contact with said plurality of peripheral strands, the latterstrands spacing the conductor rrom the sheath, and the specific gravityof the communication and tow line as a whole being less than that ofwater.

2. In a combined communication and tow line, an inner strand composed ofa plurality of high molecular weight saponified cellulose acetatethreads heavier than water, an electric conductor wrapped around saidstrand, a plurality of peripheral strands each composed of a pluralityof high molecular weight electric insulating saponifled celluloseacetate threads heavier than water, said peripheral strands beingdisposed around said inner strand and insulating said conductor, and asheath made solely of a continuous body of polyethylene lighter thanwater surrounding and in contact with said peripheral strands, thelatter strands being located between the sheath and conductor andwrapped helically around the latter, and the specific gravity of thecommunication and tow line as a whole being less than that of water.

3. In a combined communication and tow line, a central strand composedof a plurality of high molecular weight saponified cellulose acetatethreads, an electric conductor wrapped around said strand, a pluralityof peripheral strands each composed of a plurality of high molecularweight saponified cellulose acetate threads, said peripheral strandsbeing wrapped around said central strand and conductor, said strands andconductor being heavier than water, and a sheath made solely of acontinuous body of polyethylene lighter than water surrounding and incontact with said peripheral strands, the latter strands spacing theconductor from the sheath, and the specific gravity of the line beingless than that of water.

4. In a combined communication and tow line, a central strand composedof a plurality of electric insulating high molecular weight saponifiedcellulose acetate threads twisted on themselves, an electric conductorwrapped around said central strand, a plurality of peripheral strandswrapped around said central strand and conductor, each of saidperipheral strands being com- Posed of electric insulating highmolecular weight saponified cellulose acetate threads wrapped onthemselves, said central and peripheral strands and conductor beingheavier than water, and a sheath made solely of a continuous solid bodyof polyethylene lighter than water surrounding and in contact with saidperipheral strands, the latter strands spacing the conductor from thesheath, and the line as a whole having a specific gravity less than thatof water.

GEORGE E. FORSBERG.

REFERENCES CITED The following references are of record in the file of.this patent:

UNITED STATES PATENTS Number Name Date 563,274 Guilleaume July 7, 18961,978,041 Dodge Oct. 23, 1934 2,133,301 Martin Oct. 18, 1938 2,145,153Christiansen et al. Jan. 24, 1939 2,175,389 Hauif Oct. 10, 19392,235,523 Hull Mar. 18, 1941 2,319,312 Finlayson May 18, 1943 2,336,219Brown Dec. 7, 1943 2,376,813 Robins et a1 May 22, 1945 2,382,355 WarrenAug, 14, 1945 2,409,660 Briggs Oct. 22, 1946 2,418,192 Pierce Apr. 1,1947 2,424,388 Duna July 22, 1947 2,435,956 Craig Feb. 17, 19482,454,800 Hartenstein et al. Nov. 30, 1948 FOREIGN PATENTS NumberCountry Date 5,275 Great Britain of 1894 OTHER REFERENCES Sherman: TheNew Fibers (1946), page 280. (Copy in Div. 21.)

An Article: A New Dielectric for Cables, by Cratton and Slade; found inModern Plastics for July, 1944, pages -93. (A copy in P. 0. Library.)

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